The North Carolina Highway System consists of a vast network of Interstate, United States, and state highways, managed by the North Carolina Department of Transportation. North Carolina has the second largest state maintained highway network in the United States because all roads in North Carolina are maintained by either municipalities or the state. Since counties do not maintain roads, there is no such thing as a "county road" within the state. Numbering North Carolina routes may be referred to as "North Carolina Highway x", "N.C. Highway x", "NC Route x", or just "NC x", where x is the route number. North Carolina state highways numbered under 1000 are primary state highways, and numbers greater than or equal to 1000 are secondary. Nearly all secondary highways also have other names, and many primary routes are also signed with other titles. Signage Primary highways are marked by a black square sign in which is a white equilateral diamond shape with rounded corners that contains the route number. The diamond shape does not alter to accommodate larger route numbers; the numbers are reduced in size to fit within the diamond. Michigan is the only other state, aside from North Carolina, to have a near-identical route shield, but with pointed corners and an M in Michigan's shield. Secondary highways are not signed with route markers; small green or white signs are most commonly used to designate secondary roads. On these signs, the prefix "SR" for "secondary road" sometimes precedes the road number. Rules and exceptions Typically, North Carolina highway route numbers do not share numbers with any U.S. Highway or Interstate Highway in the state. If a new highway is established that would have the same number as a state highway, the state highway number usually changes. North Carolina grants exceptions to this rule in limited cases. Sometimes, as in NC 540/I-540; the two routes are given the same number because they are seen as a continuous route. Other times, as in NC 295, the number is a place holder for when the highway is eventually upgraded to an Interstate route when it meets certain standards. Finally, as in NC 73, sometimes the state, for whatever reason, does not remove a former state route designation when the Interstate is signed. Secondary roads According to NCDOT, the secondary road (SR) system of the state "consists of those roads maintained by the Department of Transportation that